Disable DVR explictly for OSP >= 15
Disable DVR explictly for OSP >= 15

Since it's enabled by default, we should explictly disable it when
someone sets --network-dvr no.

Change-Id: I31702d217194a638b72e87e2f286688da8ed1fbf

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared